1、BRITISH STANDARD Methods of measurement for equipment used in digital microwave radio transmission systems Part 2. Measurements on terrestrial radio-relay systems Section 2.5. Digital signal processing sub-system The European Standard EN 608352-5 : 1995 has the status of a British Standard BS EN BS
2、7573 : Section 2.5 : 1995 1993 60835-2-5 1995 IEC 835-2-5 : _ CENELEC ENtb0835-2-5 95 m 3404583 OLbL719 373 m BS EN 60835-2-5 : 1995 This British Standard, having been prepared under the direction of the Eiectrotechnical Sector Board, was published under the authority of the Standards Board and come
3、s into effect on 15 October 1995 O BSI 1995 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee EPI12, Radio cornunidon, upon which the following bodies were represented British Broadcastjng Corporation British Radio and Elec
4、tronic Equipment Manufacturem Association British Telecommunications plc institution of Electrical Engineers Radio, Electrid and Television Retailers Association Radiocommunications Agency The following bodies were also represented in the drathg of the standard through subcommittees and panels: ERA
5、Technology Ltd. Amendments issued since publication Amd.No. ID* The following BSI references relate to the work on this standard Committee reference EPU12 Draft for comment 91/2936 DC ISBN O 580 246% O CENELEC EN*bO35-2-5 95 3404583 OLbL20 095 = BS EN 60835-2-5 : 1995 Contents page Committees respon
6、sible Inside front cover Nationai foreword ii Foreword 2 Text Of EN 6083526 3 i BS EN 60835-2-5 : 1995 National foreword This British Standard has been prepared by Technical Committee EPL12 and is the Emh ianguage version of EN 60835-2-5 : 1995 Methods of measurement for equipment used in digital mi
7、crowave md.io tmmbsion systems Part 2: Measurements on terratriai raw-relay systems Section 5 Digital signal pcessing sub-sgstem, published by the European Committee for Eleclrotechnid Standardization (CENELEC). It is identid with IEC 835-2-5 : 1993 published by the International Electrotechnid Comm
8、ission (iEC). BS EN 60835 is published in three Parts. The other Parts are: Part 1 Measurements cmrrum to terrestrial mdw-relay systems and satellite earth stations Part 3 Memurernents on satellite earth stations Some of the many Sections of the three Parts have appeared under the number BS 7573, of
9、 the same generic title. Cross-references Publication referred to Corresponding British Standard BS EN 60835 Methods ofmem-tfor equipment used in digital microwave raw tmnsrn - measurements on the receive-signal processor are presented in clause 4; - measurements on the back-to-back connected transr
10、nitter-receiver systems are presented in clause 5. The measurements are normally taken at each input/output port, while the unused input ports are supplied by pseudo-random bit-stream (PRBS) signals, and the unused output ports are terminated with their nominal impedances. Page 6 EN 60835-2-5 : 1995
11、 METHODS OF MEASUREMENT FOR EQUIPMENT USED IN DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS Part 2: Measurements on terrestrial radio-relay systems Section 5: Digital signal processing su b-system 1 Scope This section deals with the methods of measurement on a digital radio signal processing sub-syst
12、em. The digital signal processing sub-system is, in general, able to perform the following principal functions: - multiplexing of two or more bit streams (see IEC 835-2-9, “Service Channels“, figure 1); - transmission quality evaluation for switching purposes and/or alarm indicating signal (AIS) ins
13、ertion; - coding and multiplexing of digital service channels, (see note); - scrambling and descrambling; - series-to-parallel and parallel-to-series conversion. System configurations differ, so some of the above functions may be missing, in which case only the measurements relating to those functio
14、ns present should be taken into Consideration. In digital radio-relay systems, many system configurations exist where non-hierarchical bit rates are used. In such cases, multiplex equipment is used in order to transmit more than one hierarchical bit stream and/or additional service channels (e.9. 34
15、 Mbit/s and 140 Mbit/s with bit insertion for parity bits and digital service channels, 2 x 34 Mbit/s, etc). For low bit rate systems, e.g. c 2 Mbit/s it may not be practicable to perform tests at very low BERS because of the excessively long measurement times involved. Additionally, in many. cases
16、parity bits are transmitted for quality control and switching purposes. However, as far as possible, the system should be tested at defined interface points such as those considered by the CCITT Recommendation G.703. NOTE - Digital service channels are dealt with in IEC 835-2-9. CENELEC EN*b0835-2-5
17、 95 3909583 OLbL728 386 H Page 7 EN 60835-2-5 : 1995 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this section of IEC 835-2. At the time of publication, the editions indicated were valid. All normative doc
18、uments are subject to revision, and parties to agreements based on this section of IEC 835-2 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and IS0 maintain registers of currently valid International Stand
19、ards. IEC 835-1 -2: 1992, Methods of measurement for equipment used in digital microwave radio transmission systems - Part 1 : Measurements common to terrestrial radio-relay systems and satellite earth stations - Section 2: Basic characteristics IEC 835-1 -4: 1992, Methods of measurement for equipme
20、nt used in digital microwave radio transmission systems - Pari 7: Measurements common to terrestrial radio-relay systems and satellite earth stations - Section 4: Transmission performance IEC 835-2-9: 199X, Methods of measurement for equipment used in digital microwave radio transmission systems - P
21、art 2: Measurements on terrestrial radio-relay systems - Section 9: Service channels (under consideration) CCITT Recommendation G .703: Physical/electrica/ characteristics of hierarchical digital interfaces 3 Transmlt-signal processor 3.1 Return loss See IEC 835-1-2. 3.2 Alarm characteristics 3.2.1
22、General considerations The transmit-signal processor has some alarms relating to the incoming signal and to the correct working of the processor itself. The alarm signals are, in general, used by switching equipment andlor an AIS generator. The time to initiate and to restore the alarm may be of par
23、ticular importance in the complete radio system. Below, two alarms are considered. One alarm is activated by the loss of the signal at the input of the sub-system. The other alarm is controlled by the elastic store of the sub-system in the justification process. 3.2.2 Method of measurement 3.2.2.1 i
24、oss-of-signal alarm An example of a test arrangement is shown in figure 1. CENELEC ENsb0835-2-5 95 m 34045133 OLbL729 212 Page 8 EN 60835-2-5 : 1995 The equipment under test is driven, via a switch, by a pattern generator supplying a PRES at a nominal bit rate with a defined length pattern (see CCIT
25、T Recommendation G.703). The alarm signal is displayed on an oscilloscope. By driving the switch with a low frequency (1.f.) pulse generator, it is possible to drive repeatedly the sub-system into the alarm condition, and to restore the normal condition while displaying the operate and release alarm
26、 signal on an oscilloscope. When driving the switch by a single-shot signal, it may be necessary to use a storage oscilloscope to display the result of the measurement. 3.2.2.2 Overflow alarm The measurement is made by filling the elastic store as quickly as possible in order to drive the sub-system
27、 into the alarm condition, and then measuring the time interval taken to give the alarm. This can be performed by driving the transmit-signal processor with a jittered PRBS signal with greater than maximum tolerable jitter. An example of a test arrangement is given in figure 2. The equipment under t
28、est is driven by a jitter generator. In order to use an oscilloscope without storage, it may be convenient to drive the equipment under test periodically into the alarm condition using a 1.f. pulse generator. To determine the time interval needed to initiate the alarm, it is necessary to refer to th
29、e tolerable input jitter measurement of the equipment under test. Let zj be the maximum tolerable peak-to-peak amplitude of the sinusoidal jitter at frequency 5. Driving the equipment under test with a sinusoidal jittered PRBS at frequency 5 with 5 = arj, where a i, it is possible to display the ala
30、rm operate and release. General characteristics are shown in figure 3; 5 is generally of the order of i O2 Hz to 1 O3 Hz, with a = 13. Alternatively, when the limit on the tolerable input jitter of the clock extractor circuit is less than that of the elastic store, .e. the clock extractor circuit ha
31、s a high Q-factor, it is almost impossible to drive the sub-system into the alarm condition by this method. In such a case it is necessary to stop the justification process (dashed line JP in figure 2). The measurement is then performed in the same way as described above. By stopping the justificati
32、on process, it is possible to perform the measurement independently of the Q-factor of the clock extractor circuit at the input to the transmit-signal processor, but it is generally necessary to access test points inside the equipment to do so. 3.2.3 Presentation of results The results should be pre
33、sented either as copies of the oscilloscope display or by stating the operating- and release-times of the alarm. CENELEC EN*b0835-2-5 95 W 3404583 0161730 T34 W Page 9 EN 60835-2-5 : 1995 3.2.4 Details to be specified For each alarm the following items should be included, as required, in the detaile
34、d equipment specification: a) ports at which the measurements are to be taken; b) nominal duration and tolerance to initiate the alarm following the alarm condition; c) maximum time interval to release the alarm following the restoration of the normal operating condition; d) frequency and duty-cycle
35、 if a 1.f. pulse generator signal is used to drive the switch. 3.3 Level and shape of the signal at the output of the transmit-signal processor 3.3.1 Method of measurement An example of a test arrangement is shown in figure 4. The input of the transmit-signal processor is driven by a PRBS while the
36、output is displayed on an oscilloscope. If the clock is not contained within the signal, ag. as in NRZ + Clock (CK), the data signal and the clock should be displayed at the same time on a dual-trace oscilloscope. The level and shape of the signals and the delay between the data signal and the clock
37、 should be measured. NOTE - With reference to figure 5, in the case of a clock signal with a 50 % duty-cycle and little distortion it is easier to measure c instead of T. 3.3.2 Presentation of results The results should be presented as a copy of the oscilloscope display. 3.3.3 Details to be specifie
38、d The following items should be included, as required, in the detailed equipment specification: a) ports at which the measurements are to be taken; b) bit rate and its tolerance; c) code, e.g. NRZ + CK; d) test load impedance; e) mask of the pulses (see figure 5), and in particular: - level and shap
39、e of the data pulse between two spaces; - maximum voltage of a space; - mask of the clock; - tolerance in the relative positions of data and clock (see delay z and z in figure 5). CENELEC ENrbQ835-2-5 95 3404583 OLL1731 970 Page 10 EN 60835-2-5 : 1995 3.4 See IEC 835-1-4. Jitter at the output of the
40、 transmit-signal processor Generally, only the output jitter measurement is required and can be carried out with normal instrumentation. Normally, the other two types of jitter measurement (tolerable input jitter and transfer function) are not required. 4 Receive-signal processor 4.1 4.1.1 Method of
41、 measurement Acceptability of the input signal The equipment specifications establish the requirements for the signal at the output ports of the sub-systems. The following sub-system, in general connected by a suitable cable, should be capable of accepting at the input port a signal which may have b
42、een distorted and attenuated in a controlled manner. In general, the measurement is carried out with the transmit-signal processor and the receive-signal processor connected as shown in figure 6. The input of the receive-signal processor is driven by a PRBS via a suitable cable. The oscilloscope pro
43、vides a check on the signal at the input and output of the cable. The sub-system shall work without errors. 4.1.2 Presentation of results A statement that the sub-system under test is able or unable to pass the test. 4.1.3 Details to be specified The following items should be included, as required,
44、in the detailed equipment specification: a) ports at which the measurements are to be taken; b) bit rate and its tolerance; c) code, e.g. NRZ + CK; d) test load impedance; e) length and type of cable; f) maximum permitted relative delay time between data and clock (when the code is such that they ar
45、e separated, as in NRZ + CK); g) minimum permitted value of return loss at the input port(s); h) minimum acceptable time during which no errors are recorded, e.g. the number of minutes in order to reach a suitable confidence on a low BER measurement (e.g. lo-), taking into account the bit rate. CENE
46、LEC ENub0835-2-5 75 m 3404583 0163732 807 Page 11 EN 60835-2-5 : 1995 4.2 Return loss See IEC 835-1-2. 4.3 Alarm characteristics 4.3.1 loss-of-signal alarm This measure has already been dealt with in 3.2 above concerning the transmit-signal processor. 4.3.2 Overflow alarm The code of the signal at t
47、he input of the receive-signal processor generally has separate data and clock (e.g. NRZ + CK). This means that there is no clock extractor circuit at the input of the receive-signal processor, and consequently it is always possible to drive the sub-system into the over- flow alarm condition by a su
48、itable jittered input signal without access to internal test points in the equipment. The measurement is explained in 3.2 above. 4.4 This measurement has already been treated in 3.3 concerning the transmit-signal pro ces sor . Level and shape of the output signal 4.5 Output jitter in the absence of
49、input jitter See IEC 835-1-4. Generally, only output jitter measurements are required and these can be made with normal instrumentation. Sometimes the other two types of jitter measurement (tolerable input jitter and jitter transfer function) are required, and in such cases special instrumentation is needed, since the input of the receive-signal processor may not have standardised interface characteristics (e.g. non-hierarchical bit rates). 5 Transmitter-receiver measurements This group of measurements refers to characteristics (e.g. absolute delay time, j
